MOLGULA MANHATTENSIS 259 



reality, in cavities reduced to mere crevices communicating with 

 each other. These crevices represent the modified body cavity 

 and are called schizoccele. The latter should not be confused 

 with the cavity surrounding the pharynx. This cavity, com- 

 posed of a right and left half separated from each other by the 

 adhesion of its wall along the dorsal lamina and endostyle, is 

 called the peripharyngeal or peribranchial cavity and represents 

 nothing but two blind sacs of the cloacal chamber. Being blind 

 sacs they of course possess an inner and outer wall. The in- 

 testinal loop and all other organs pressed to the one or the other 

 side of the pharynx lie in the schizoccele, to the outside of the 

 outer wall of the peripharyngeal cavity. 



Digestive system. We have seen already that the in- 

 current siphon leads into an enormous pharynx and that the 

 passage to the latter is protected by a transverse sieve formed by 

 twelve branched tentacles. The pharynx is a very complicated 

 organ which functions both as pharynx and gill, and it presents 

 many peculiar structures. There is, not far from the tentacular 

 sieve, a circular ciliated peripharyngeal groove formed by two 

 circular ridges. The endostyle, the dorsal lamina and the six 

 pairs of pharyngeal ridges begin at this groove. The dorsal 

 lamina is a straight ridge running in the mid-dorsal line from the 

 peripharyngeal groove to the opening of the oesophagus. The 

 endostyle begins at the opposite pole of the peripharyngeal groove 

 and runs in the mid-ventral line to within a short distance from 

 the opening of the oesophagus. The endostyle is a deep ciliated 

 groove formed, like the peripharyngeal groove by two ridges. 

 Each ridge has three ciliated bands separated from each other 

 by simple epithelial cells. The cells at the bottom of the groove 

 possess extraordinarily long cilia which reach beyond the edges 

 of the ridges. Between the end of the endostyle and the oesoph- 

 agus is a fine inferior groove. Starting from the peripharyn- 

 geal groove and evenly interspaced between the dorsal lamina 

 and the endostyle are six pairs of pharyngeal ridges which end in 

 the inferior groove. They are curved in the same sense as the 



